The present invention relates to a charge-controlling agent for controlling chargeabilities of toners used for electrophotography, electrostatic recording, electrostatic printing, and the like. The invention also relates to a toner using the charge-controlling agent.
In copying machines and printers utilizing the principle of electrophotography, a developing method is employed wherein a dry toner charged beforehand is fed to an electrostatic latent image formed on an electrophotographic photosensitive body to form a visible image. Generally, in the dry toner, the surface of toner particles is charged by friction between the toner particles in the case of single-component system in which a magnetic powder such as iron powder is internally incorporated into the toner particles. In the case of two-component system, the surface of toner particles is charged by mixing and stirring toner particles with a magnetic powder. Charging properties such as initial chargeability, stability of charge-level with the lapse of time, and saturated charged amount of the toner particles considerably affect the quality of electrostatic print. Therefore, for controlling always these physical properties and maintaining a stable state, a positively chargeable or negatively chargeable charge-controlling agent is frequently added in toner particles at the production of the particles.
As a charge-controlling agent which imparts chargeability to black toners, nigrosine has been hitherto employed. However, nigrosine has a strong coloring power and adversely affects hue of color except black, so that it is difficult to apply it to color toners whose demand has been recently increasing.
Moreover, safety requirement of chemical substances becomes gradually severe in recent years. Even in the case of charge-controlling agent, it is required to reduce volatile organic compounds (VOC) as much as possible, which generate upon kneading with a toner resin or upon actual high-speed printing on a copying machine. However, nigrosine contains a trace amount of aniline and complete removal of aniline is difficult, so that there is a possibility that the use of nigrosine containing a trace amount of smelly and harmful aniline may be regulated in future.
As charge-controlling agents other than nigrosine, there are mentioned, for example, quaternary ammonium salts disclosed in JP-A-62-53944 (corresponding to U.S. Pat. Nos. 4,683,188 and 4,780,553)(The term xe2x80x9cJP-Axe2x80x9d used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) and JP-A-3-27052, a polyamine having a repeating unit wherein a pyrrole ring or phenylimino group and a piperazine ring or imino group are bonded through methylene group described in JP-A-51-9456 (corresponding to U.S. Pat. No. 4,021,358), a polyamine having a repeating unit wherein a phenylimino group and a piperazine ring are bonded through methylene group described in JP-A-58-171060, and a polyamine selected from the group consisting of poly(phenylimino) and poly(alkylimino) disclosed in JP-A-6-348061 (corresponding to U.S. Pat. No. 5,491,043).
The quaternary ammonium salts disclosed in JP-A-62-53944 (corresponding to U.S. Pat. No. 4,780,553) and JP-A-3-27052 are colorless or light in color, so that it is possible to employ them as charge-controlling agents. However, these compounds have drawbacks that thermal stability is insufficient and thus, the compounds tend to cause thermal decomposition and coloring, when kneading with a binder resin for toner, and also chargeabilities are considerably inferior as compared with nigrosine.
Moreover, the polyamine disclosed in JP-A-6-348061 (corresponding to U.S. Pat. No. 5,491,043) has a drawback that it is a compound having a low melting point and thus, tends to be colored, when kneading with a toner resin, and therefore, it is difficult to employ it as a charge-controlling agent for color toners. Furthermore, the polyamines disclosed in JP-A-51-9456 (corresponding to U.S. Pat. No. 4,021,358) and JP-A-58-171060 cause almost no coloring but have drawbacks that thermal decomposition occurs, when kneading with a binder resin for toner, they have considerably poor dispersibility in a toner resin, and they are not always excellent in chargeabilities. As described above, there has not yet been found a charge-controlling agent which is colorless or light in color, has excellent chargeabilities, is applicable to color toners, and also emits only a little amount of VOC.
An objective of the present invention is to provide a charge-controlling agent which can be applied to not only black toners, but color toners, emits only a little amount of VOC, and is excellent in chargeabilities, particularly in charged amount and stability of charge-level.

Another objective of the present invention is to provide a toner comprising the charge-controlling agent.
Other objectives and effects of the present invention will become apparent from the following description.
For solving the above problem, the invention provides:
(1) a charge-controlling agent comprising a polyamine having a repeating structure represented by the following general formula (I): 
wherein R1 to R4 each independently represents an alkyl group having 1 to 4 carbon atoms or hydrogen atom, n represents 0 or 1, and
when n=0, R5 represents an alkylene group having 4 to 15 carbon atoms, which may have a substituent selected from the group consisting of alkyl groups having 1 to 4 carbon atoms and phenyl group, and
when n=1, A represents a phenylene group in which the hydrogen atom(s) on the ring may be replaced by alkyl group(s) having 1 to 4 carbon atoms, and R5 and R6 each independently represents an alkylene group having 1 to 8 carbon atoms, provided that the sum of the carbon atoms of the alkylene groups represented by R5 and R6 ranges from 2 to 9.
The charge-controlling agent of the invention comprises a polyamine having a repeating structure represented by the above general formula (I). In the above general formula (I), R1 to R4 each independently represents an alkyl group having 1 to 4 carbon atoms or hydrogen atom, and n represents 0 or 1.
In the case that n is 0, R5 represents an alkylene group having 4 to 15 carbon atoms, which may have a substituent selected from the group consisting of alkyl groups having 1 to 4 carbon atoms and phenyl group. Examples of such a case of R5 include linear alkylene groups such as butylene group, pentamethylene group, hexamethylene group, heptamethylene group, octamethylene group, nonamethylene group, decamethylene group, undecamethylene group, dodecamethylene group, tridecamethylene group, tetradecamethylene group, and pentadecamethylene group; alkylene groups in which part of hydrogen atoms is replaced by substituent(s) selected from the group consisting of methyl group, ethyl group, propyl group, butyl group, and phenyl group; and the like. Among these alkylene groups, preferred is a linear alkylene group having 4 to 15 carbon atoms, and particularly preferred is a linear alkylene group having 6 to 12 carbon atoms.
In the above general formula (I), two or more of R5 may be the same or different from each other in the case that n is 0. Also, the polyamine may be a polyamine wherein two or more of R5 is composed of a combination of a small amount of an alkylene group having a small number of carbon atoms such as methylene group, ethylene group, or propylene group and an alkylene group having a large number of carbon atoms such as hexamethylene group or decamethylene group. However, in such a combination case, the use of too high ratio of methylene group results in a polyamine which has a high melting point and is very hard, so that the dispersibility into a binder resin tends to be poor in the kneading process. Also, the use of too high ratio of ethylene group or propylene group results in a polyamine which has strong hydrophilicity owing to piperazine group and thus strong affinity with water, so that the polyamine adsorbs the moisture in air at its mixing with a toner and therefore, the charged amount tends to decrease. Accordingly, in the case of combined use of an alkylene group having a small number of carbon atoms, the ratio of the alkylene group having a small number of carbon atoms is preferably 10 mol % or less relative to all of R5.
On the other hand, in the above general formula (I), a polyamine wherein n is 0 and all of R5 are methylene groups has a high melting point and is very hard, so that the dispersibility into a binder resin is poor in the kneading process, and thus, it is impossible to use.
In the case that n is 1, A represents a phenylene group in which hydrogen atom(s) on the ring may be replaced by alkyl group(s) having 1 to 4 carbon atoms, and the phenylene group may be any of p-phenylene group, m-phenylene group, or o-phenylene group, but particularly preferred is p-phenylene group. R5 and R6 each independently represents an alkylene group having 1 to 8 carbon atoms, but sum of the carbon atoms of the alkylene groups of R5 and R6 ranges from 2 to 9.
In the case that n is 1, examples of R5 and R6 include methylene group, ethylene group, propylene group, butylene group, pentamethylene group, hexamethylene group, heptamethylene group, and octamethylene group.
In the above general formula (I), preferred is a polyamine wherein n is 0, all of R1 to R4 are hydrogen atoms, and R5 is a linear alkylene group having 4 to 15 carbon atoms, and particularly preferred is the polyamine wherein R5 is a linear alkylene group having 6 to 12 carbon atoms. Also, in the above general formula (I), particularly preferred is a polyamine wherein, n is 1, all of R1 to R4 are hydrogen atoms, A is p-phenylene group, and both of R5 and R6 are methylene groups.
In general, a polyamine for use in the invention can be easily produced by dissolving a compound having a piperazine skeleton in an organic solvent, adding dropwise a dihalide such as a dihalogenoalkane or an alkane-disulfonate compound such as hexane-1,6-di-p-toluenesulfonate thereto at an elevated temperature to effect the reaction therebetween, and then neutralizing the resulting product with an alkali.
The compound having a piperazine skeleton for use as a synthetic raw material of the polyamine is not particularly limited as far as the secondary amino groups of the piperazine skeleton are reactive and the carbon atoms of the skeleton have hydrogen atom(s) or alkyl group(s) having 1 to 4 carbon atoms. Examples of such a compound having a piperazine skeleton include piperazine, 2-methylpiperazine, 2-butylpiperazine, 2,3-dimethylpiperazine, 2,3,5-trimethylpiperazine, 2,3,5,6-tetramethylpiperazine, and the like. Among them, particularly preferred are piperazine and 2-methyl piperazine. Moreover, these compounds having a piperazine skeleton may be used solely or in combination.
Examples of the dihalide for use as a synthetic raw material of the polyamine include 1,4-dichlorobutane, 1,5-dichloropentane, 1,6-dichlorohexane, 1,7-dichloroheptane, 1,8-dichlorooctane, 1,9-dichlorononane, 1,10-dichlorodecane, 1,11-dichloroundecane, 1,12-dichlorododecane, 1,13-dichlorotridecane, 1,14-dichlorotetradecane, 1,15-dichloropentadecane, 1,6-dibromohexane, 1,8-dibromooctane, 1,6-diiodohexane, 2,2-dimethyl-1,3-dichloropropane, p-xylylene dichloride, m-xylylene dichloride, o-xylylene dichloride, and the like. Among them, particularly preferred are 1,6-dichlorohexane, 1,8-dichlorooctane, and 1,10-dichlorodecane.
These dihalides may be used solely or in combination. In the case that the ratio of the dihalides having a small number of carbon atoms such as dichloromethane, 1,2-dichloroethane, or 1,3-dichloropropane is high, especially in the case that dichloromethane is used, the resulting polyamine has an increased melting point, and the dispersibility into a binder resin tends to be poor at the kneading of the polyamine with the binder resin. Also, in the case that especially 1,2-dichloroethane or 1,3-dichloropropane is used, the resulting polyamine maintain strong affinity with water, so that the polyamine adsorbs the moisture in air at its mixing with a toner and therefore, the charged amount tends to decrease. Accordingly, in the case that a dihalide having a small number of carbon atoms, it is preferable to use the dihalide having a small number of carbon atoms in combination with other dihalide such as 1,6-dichlorohexane or 1,10-dichlorodecane. In the case that the dihalide having a small number of carbon atoms is used, the ratio of the dihalide is preferably 10 wt % or less relative to total dihalides.
Examples of the alkane-disulfonate compound for use as a synthetic raw material of the polyamine include butane-1,4-di-p-toluenesulfonate, hexane-1,6-di-p-toluenesulfonate, octane-1,8-di-p-toluenesulfonate, and the like. Among them, particularly preferred is hexane-1,6-di-p-toluenesulfonate.
Moreover, the molar ratio of the above compound having a piperazine skeleton to the dihalide or alkane-disulfonate compound is preferably in the range of 0.5 to 2.0, particularly preferably in the range of 0.8 to 1.5.
Furthermore, after the compound having a piperazine skeleton and the dihalide or the like have been subjected to a predetermined reaction, the resulting polyamine wherein an imino group is left at the ends may be used after reacting it with a small amount of formalin. At that time, when the ratio of formalin is too high, the melting point of the resulting polyamine is raised and the dispersibility into a binder resin tends to be poor at the kneading. Therefore, the ratio is preferably 10 mol % or less relative to total alkylenes.
The number-average molecular weight of the polyamine for use in the invention is preferably in the range of 500 to 100,000, particularly preferably in the range of 5,000 to 30,000. In the case that the number-average molecular weight of the polyamine is less than 500, the polyamine has a low melting point and tends to fly, when kneading during the conversion to a toner. In the case that the number-average molecular weight of the polyamine exceeds 100,000, the dispersibility at the above kneading tends to be poor. Thus, the both cases are not preferred.
The charge-controlling agent comprising a polyamine having a repeating structure represented by the general formula (I), which is used in the invention, is useful as a positively chargeable charge-controlling agent for controlling chargeabilities of toners for use in electrophotography and the like.
The method for incorporating the charge-controlling agent of the invention into a toner is not particularly limited. For example, there may be mentioned a method wherein a compound to be used as a charge-controlling agent is preliminary pulverized and, after further classification, if necessary, the resulting powder is mixed and kneaded with a toner resin, a colorant, and other toner-constituting components.
The amount of the charge-controlling agent of the invention at the incorporation into a toner is preferably in the range of 0.1 to 15 parts by weight, particularly preferably in the range of 0.5 to 10 parts by weight relative to 100 parts by weight of a toner resin. In the case that the ratio of the charge-controlling agent in the toner is less than 0.1 part by weight, initial chargeability is deteriorated or the toner tends to fly. On the other hand, in the case that the ratio of the charge-controlling agent in the toner exceeds 15 parts by weight, the stability of charge-level tends to be poor. Thus, the both cases are not preferred.
A positively chargeable toner can be obtained by adding the charge-controlling agent of the invention in accordance with the above method. Moreover, other charge-controlling agent may be used in combination unless the performance of the above charge-controlling agent and the purpose of the toner are deteriorated. The charge-controlling agent of the invention may be also used together with a negatively chargeable charge-controlling agent if necessary for controlling the charged amount, and thus, it is possible to use as a charge-controlling agent for not only a positively chargeable toner but also a negatively chargeable toner.
As a toner resin (binder resin) for use in the toner of the invention, any of the hitherto known toner resins used for electrophotography may be employed without particular limitation. Examples of such toner resins include styrene resins such as polystyrene, styrene-(meth)acrylate copolymers, styrene-(meth)acrylate-acrylonitrile copolymers, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, and styrene-maleic acid copolymer, polyester resins, epoxy resins, (meth)acrylic resins, phenol resins, xylene resins, vinyl chloride resins, polyurethane resins, polyvinyl butyral resins, and the like. Among them, particularly preferred are styrene-(meth)acrylate resins and polyester resins. Generally, one of these resins is employed but two or more of them may be employed, if necessary.
As colorants for use in the toner of the invention, hitherto known various organic pigments, inorganic pigments, dyes, and the like may be employed. Specific examples thereof include black pigments such as carbon black; blue pigments such as phthalocyanine blue, aniline blue, and ultramarine blue; green pigments such as malachite green, phthalocyanine green, and brilliant green; red pigments such as rose bengal, permanent red, irgasine red, and toluidine red; yellow pigments such as benzidine yellow, quinoline yellow, fast yellow G, and hanza yellow; triaryl methane dyes, azo dyes, nigrosine dyes, and the like.
To the toner of the invention, hitherto known additives such as higher fatty acid and metal salts thereof, natural or synthetic waxes, and the like may be added, if necessary.
The toner of the invention is applicable to both of a two-component developer and a single-component developer. For example, in the case that the toner of the invention is used as two-component developer, the toner is used in combination with carrier powder. Examples of the carrier powder for use therein include magnetic powders such as iron powder, ferrite powder, and nickel powder, glass beads, and the like, as well as coating carriers obtainable by treating the surface of the above carrier powders with a resin.
In the case that the toner of the invention is used as a single-component developer, there may be used a dispersion obtainable by adding an appropriate amount of a magnetic fine powder such as iron powder or ferrite powder at the production of the toner, or a non-magnetic single-component type containing no magnetic powder.
The polyamine represented by the general formula (I) for use as the charge-controlling agent of the invention has a considerably high charge level as compared with the quaternary ammonium salts hitherto used, and is highly excellent in stability of charge-level with the lapse of time as compared with nigrosine. Moreover, since the polyamine is light in color, it is extremely useful as a charge-controlling agent for not only black toners but also color toners.